Although not everyone trusts Ubuntu these days, but from a certain time, Canonical has been very serious about their Ubuntu One (which is their version of the open-source cloud model) product module and its behavior. Although they had a dedicated app for the Android "crowd" for sometime now but...
... since Apple is seemingly becoming powerful day by day, they too introduced their version of Cloud computing model called iCloud recently, it's about time that Ubuntu One has finally decided to make an app that lets Apple "i-geeks" :) to interact with the Ubuntu One Music account.
It's free right?
Well, the application is free but after the initial 30 days of trial period, you'll have to pay a monthly charge of $3.99. This is not a criticism since giving away 20GB storage for free doesn't make any sense, nor it'll survive if it has no way to cover its expenses as anyone can see. And the Ubuntu One Music account lets you deal with MP3, Ogg Vorbis and non-DRM iTunes.
Although not everyone would like it but I think almost all of us GNU/Linux geeks just love the fact that Ubuntu respectively filter-out the DRM "license" which as said, it's better to be in the cloud still retaining some of the original ideas that took us this far rather than live outside of it and be miserable (or maybe not :D).
*. It only supports music streaming over Wi-Fi or 3G (of course).
*. MP3, Ogg Vorbis and non-DRM iTunes files are supported.
*. Supports iOS 3.1 or higher.
*. Automatic playback resume (if it was interrupted, say due to a call).
*. 30 days of "fun time", $3.99 afterwards (each month that is :D).
*. Shuffle and repeat ... are just a few to mention.
You can get the app from both this Ubuntu One Music page or from this Apple iTunes app store page. Good luck.